The present invention relates generally to optical devices, and particularly relates to methods of making devices incorporating prefabricated optical fibers. More particularly, the invention also relates to integrated optic chips (IOCs) with embedded optical fibers and carved-out regions for mounting or creating other components therein.
Integrated optic chips consist of different elementary waveguide circuits such as straight waveguides, couplers, branches, and bends. Depending on the type of material used in fabrication of the waveguide they can perform different functions such as light generation, amplification, modulation, splitting and so on. One important family of IOCs are silica-based planar integrated circuit devices that perform mostly passive operations such as coupling, splitting and filtering.
Two exemplary methods for fabricating silica based IOCs are flame hydrolysis and ion exchange, which yield low loss waveguide devices. However, making waveguide grating devices in waveguides made by these methods is difficult and expensive. Waveguide gratings are important for providing functions such as narrow band filtering and adding, dropping and routing wavelengths.
One attractive method for fabricating waveguide devices with gratings is by direct creation (writing) of waveguides by illuminating with electromagnetic radiation exposed areas in a thin film of photosensitive material such as organically modified glasses. However, this technology may not be suitable for mass fabrication and the waveguides made thereby may suffer from excess propagation losses compared with commercially entrenched waveguide fabrication techniques. Another disadvantage is that one-stage fabrication of large area integrated optic circuits with crowded elements is risky and results in low yield and therefore high cost.
Prefabricated standard optical fibers are to date the best known type of optical waveguide to guide light with very low propagation loss. It is also possible to write gratings on optical fibers and utilize them in all-fiber circuits with the desired functions. But a major deficiency of all-fiber circuits is that optical fiber pieces used either as a waveguide or a waveguide with grating are not flexible enough to be connected together in a compact form. Moreover, some of the optical elements cannot be made using fibers consistently. A desirable integrated optic technology would offer the necessary flexibility to make some of the optical elements that are difficult to build with fibers while also providing optical connection at the board level utilizing the flexibility of integrated optical waveguides.
A reliable and economic technology that can offer the advantages of both all-fiber made devices and the flexibility of planar optical waveguides for optical interconnection and the fabricating of those devices that are best implemented by planar waveguides, such as branches and couplers, is desirable. It is also desirable to have the capability of fabricating the optical elements in successive independent stages, possibly from different materials and with different processes.
Regardless of the fabrication method of an integrated optic circuit on a substrate there is the problem of attaching fibers to waveguides in an economical way. The prior art has addressed the subject of how to attach a fiber to a waveguide. The best known method of attaching fibers to waveguides uses etched V-grooves to position the fiber in front of the waveguide. For instance, in U.S. Pat. No. 5,175,781 xe2x80x9cAttaching Optical Fibers To Integrated Optic Chipsxe2x80x9d, issued Dec. 29, 1992 to Hockaday et al., there is disclosed a method of attaching fiber to integrated optic chips by forming aligning grooves, using laser ablation, on the IOC followed by cutting the surface ends of the waveguides by a dicing saw and then disposing the optical fibers within the grooves and securing them with adhesives to attach the fibers to the IOC permanently. Disadvantages of such methods are that they are labour intensive, cannot assure perfect alignment of fibers and planar waveguides in all directions, and that they introduce excess losses due to a mismatch between the core size of the optical fiber and the waveguide. It is therefore also desirable to provide a method of attaching fibers to a waveguide circuit which is less time consuming, has lower excess loss, is more reliable, and is amenable to being automated.
The present invention endeavours to mitigate some of the above-mentioned problems of IOC fabrication.
In the present invention, optical fibers are first embedded in a substrate and are precisely placed in predetermined positions by lithography, molding, laser, chemical or mechanical micromachining, their positions being readable with the aid of markers on the front and possibly back surfaces of the substrate defining a metric system for locating the fibers precisely in both lateral directions. The fibers are affixed in the grooves by adhesives or the like; then strips of the substrate with fibers embedded therein are cut from the left and right sides. The left and right separated sections, with the embedded fibers and extra lengths of loose fibers protruding beyond the edges of these sections, are end polished, if necessary, and kept for later re-attachment to the substrate with the embedded fibers used as the input/output connectors. The remaining section, referred to here as xe2x80x9cIntegrated Optical Boardxe2x80x9d (IOB) when finished, is then carved to an appropriate depth in designated areas and filled or coated (by dip coating or other methods) with layers of suitable materials from which a waveguide device can be fabricated. The waveguide will connect the input/output fibers optically with the patterns of waveguide circuits by using the markers to find the exact location of the embedded fibers in the IOB. Alternatively different areas of the carved IOB can be filled or coated with different materials such that the waveguide devices made of these material will perform different functions. If necessary, using a dicing saw, the end faces of the embedded fibers and the fabricated waveguides are cut and polished at an angle to reduce the coupling losses and optical reflection from the interfaces of sections with different refractive indexes. Having completed the optical interconnection of the different points in the IOB, the two right and left connectors are re-attached to the IOB by perfectly aligning the end faces of the fibers inside the connectors and the fibers inside the IOB.
Thus, fast or automatic alignment of fibers to IOCs is achieved. Further, fiber based devices are easily integrated with planar optical waveguides in one substrate.
In a method aspect of the present invention an optical fiber is first secured in a groove in the surface of an optic substrate, which is subsequently processed to create requisite integrated optic components in portions thereof.
After the optical fiber has been secured in the groove, opposite optic substrate ends may be excised to serve as optical connectors to the remaining central portion after its processing has been completed. For convenience, the central portion, once processing has completed, is hereafter refereed to as an integrated optic board (IOB).
In a preferred aspect of the present invention, the central portion of a substrate, having embedded fibers therein, is processed by: polishing or removing its top layer all down to the top of the fibers"" cores; carving out a predefined region, or regions, in its top layer down to a depth at least exposing part of the fibers"" cores; and filling or coating the carved out region, or regions, with an optical material or materials in one or more layers, one of which may be photosensitive, for creating a planar optical waveguide or other optical components therein; thereby providing an IOB interconnectable to other devices through the embedded optical fibers.
The step of removing the top layer off may be omitted at the risk of increasing the tolerance in the depth of the carved out region.
The method of the present invention also incorporates applying a plurality of surface markers to the optic substrate prior to processing for subsequent alignments.
An optical device according to the present invention comprises at least an IOB having an integrated optic component therein and an embedded optical fiber and a connector also having an embedded optical fiber characterized in that both the IOB and the connector were excised from the same or similar optic substrate after the optical fiber has been embedded therein, thereby providing optimal alignment between connector and IOB.
In another device aspect, the present invention provides an integrated optic chip, comprising: a planar optical waveguide in at least one upper layer region of an optic substrate; and an optical fiber fully embedded in another upper layer region of the optic substrate and coupled at one end thereof to one end of the planar optical waveguide.